<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .container{
            font-size: 50px;
            color: black;
        }

        /* 当屏幕尺寸小于等于1200px时 */
        @media screen and (max-width:1200px) {
            .container{
                font-size: 40px;
                color: red;
            }
        }

        /* 当屏幕尺寸小于等于900px时 */
        @media screen and (max-width: 900px) {
            .container{
                font-size: 30px;
                color: blue;
            }
        }

        /* 当屏幕尺寸小于等于700px时 */
        @media screen and (max-width:700px) {
            .container{
                font-size: 20px;
                color: green;
            }
        }
    </style>
</head>
<body>
    <div class="container">
        Web前端开发
    </div>
</body>
</html>